Sealed envelope examining device for detecting the presence of metal

ABSTRACT

A device for detecting the presence of metal in sealed flat envelopes, whereby the presence of &#39;&#39;&#39;&#39;letter bombs&#39;&#39;&#39;&#39; and similar destructive devices can be sensed and an alarm device actuated. The device includes a base of generally rectangular configuration containing a detecting circuit including a pair of coils, one of said coils being mounted within said base, and the other said coil supported on a bridge-like structure extending transversely above said base to define an interstice through which envelopes pass. The presence of metal changes the electromagnetic field existing between the coils, resulting in a change in impedance sufficient to actuate the alarm.

United States Patent 1 91 Kulik et al.

[ SEALED ENVELOPE EXAMINING DEVICE FOR DETECTING THE PRESENCE OF METAL[76] lnventors: Herbert S. Kulik; Jacob Schachter,

both of 100 Ricefield Ln,

Hauppauge, NY.

[22] Filed: Feb. 28, 1974 [2]] Appl. No.: 446,698

[52] US. Cl. 324/41 [51 Int. Cl G01r 33/00 [58] Field of Search 324/41[56] References Cited UNITED STATES PATENTS 2,966,582 l2/l960 Wachtel324/41 OTHER PUBLICATIONS Greenmeyer', P., Electronic Metal Detector,Electronic Industries & Electronic Instrumentation, Nov.

14 1 July 1,1975

1947, pp. 9, 10 & 13.

Primary ExaminerRobert J. Corcoran Attorney, Agent, or FirmCharles E.Temko [57] ABSTRACT A device for detecting the presence of metal insealed flat envelopes, whereby the presence of letter bombs and similardestructive devices can be sensed and an alarm device actuated. Thedevice includes a base of generally rectangular configuration containinga detecting circuit including a pair of coils, one of said coils beingmounted within said base, and the other said coil supported on abridge-like structure extending transversely above said base to definean interstice through which envelopes pass. The presence of metalchanges the electromagnetic field existing between the coils, resultingin a change in impedance sufficient to actuate the alarm.

2 Claims, 7 Drawing Figures ENTFUJUL] sugar FlG.2

FIG.4

SEALED ENVELOPE EXAMINING DEVICE FOR DETECTING THE PRESENCE OF METALBACKGROUND OF THE INVENTION Metal detecting devices are per se known inthe art, and have been used extensively in the detection of land minesand similar buried metallic objects. More recently, devices have beenused at air terminals for the examination of passenger baggage andfreight. Such devices generate a relatively wide electro-magnetic field,and are not optimized for detecting relatively small metallic articlesor devices used in the construction of socalled letter bombs," neitherare they physically convenient to use for this function. They may alsobe unsafe to use because of excessive field power.

With wide use of such destructive devices sent through postal channels,there has arisen a need for a simple device through which letters andenvelopes may be passed at high speed for the purpose of metallicdetection. Many letter bombs are formed from flattened cartridge casesin conjunction with spring wire, and the total metallic content of asingle device is relatively small. Other types are electrically operatedand use metallic parts such as batteries, wires, foil, switches anddetonators.

BRIEF DESCRIPTION OF THE PRESENT INVENTION Briefly stated, the inventioncontemplates the provision of a letter box size detector comprising agenerally rectangular base enclosing a detector circuit and a first coilforming a part thereof. A transversely extending bridge is supported bysaid base and encloses a second coil forming a part of the detectorcircuit, the bridge defining with the base an interstice between whichletters and envelopes are serially passed. The letters are placed upon asliding drawer and move horizontally beneath the bridge, or in the caseofa large number ofletters, the base may be tilted to form an inclinedplane, and the letters allowed to fall under the action of gravitythrough the interstice. To maintain privacy, a pivotally mounted coverselectively overlies the drawer, and such position, the cover locks thedrawer against withdrawal.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings, to which referencewill be made in the specification, similar reference characters havebeen employed to designate corresponding parts throughout the severalviews.

FIG. 1 is a side elevational view of an embodiment of the invention.

FIG. 2 is a first end elevational view thereof.

FIG. 3 is a second end elevational view thereof.

FIG. 4 is a top plan view thereof.

FIG. 5 is a second top plan view with cover and drawer elements inopened condition.

FIG. 6 is a view in perspective of the embodiment with cover and drawerelements removed, and the base supported at an angle wherein an uppersurface thereof forms an inclined plane.

FIG. 7 is a schematic wiring diagram of the detector circuit forming acomponent of the embodiment.

DETAILED DESCRIPTION OF THE DISCLOSED EMBODIMENT In accordance with theinvention, the device, generally indicated by reference character 10includes a base element 11 of generally rectangular configuration andcomprising a lower wall I2, side walls I3 and I4, end walls 15 and I6and an upper wall 17. Extensions I8 on the side walls 13 and 14 supporta hollow bridge 19 supporting in concealed relation a first coil l9 (seeFIG. 4) immediately above a second coil not shown) disposed in the baseelement I], the bridge 19 forming with the upper surface of the upperwall 17 a transversely extending space 21 through which letters orenvelopes being examined may pass.

Slidably mounted between the side walls 13 and I4 is a drawer element22, the element 22 including an outer end wall 23, a bottom wall 24 andan inner end wall 25. The longitudinal edges of the bottom wall 24 ridein guiding grooves 26 (see FIGS. 5 and 6) so that the lower surfacethereof is free of contact with the upper surface of the wall 17 duringmovement.

Supported by hinge means 27 and 28 is a pivotally mounted cover element29 including a curved end wall 30, a planar main wall 31 and a firsttransverse member 32 having detent means 33 at each end resilientlyengageable in corresponding recesses 34 in the side walls 13 and 14. Asecond transverse member 35 includes a surface 36 adapted to engage aninwardly disposed wall of the inner end wall 25, and maintain it in theposition shown in FIG. 4.

The device may be operated in either of two manners, depending upon thequantity of letters and envelopes to be examined. In one method, thecover element 29 is swung open as shown in FIG. 5, and one or moreletters are placed on the upper surface of the wall 24. After activatingthe detector circuit, the drawer is withdrawn as shown in FIG. 5,causing the envelopes to pass beneath the bridge 19, the presence ofmetal being thereby detected.

Where a relatively large number of pieces of mail are to be examined,the drawer element 22 and cover element 29 are removed, and the baseelement II is propped using a selectively engageable wire frame member38 to the position shown in FIG. 6. Pieces of mail are merely dropped onthe inclined upper surface of the upper wall I8 to fall under the actionof gravity beneath the bridge I9 effecting a similar result.

Referring to FIG. 7 in the drawings, there is illustrated atransistorized circuit suitable for use in the disclosed embodiment, itbeing understood by those skilled in the art that other circuits of wellknown type may be substituted where desired.

Referring to FIG. 7, transistor 42 is an oscillator with a tuned circuitconsisting of coil 43 and a 0.0 l 5 capacitor 44 operating at afrequency of approximately 20 KHz. Feedback is provided by coil 45.

When a metallic object is inserted between coil 43 and coil 45, thefeedback is disturbed and the level of the oscillator decreases. Thesensitivity of the circuit is adjusted by means of a 5K reheostat 46.

The output of the oscillator 42 is amplified and detected by transistor47. The level at the collector of transistor 47 is compared with thelevel of the 5K reheostat 46 setting. When the anode of transistor 48rises 0.3 volt above the potentiometer setting, transistor 48 conductsand triggers a silicon controlled rectifier 49 which, when conducting,causes the alarm 50 to sound.

Integrated circuit 51 is a voltage regulator which provides a stablevoltage. The power supply 52 is a battery of two 9 volt rechargeablebatteries. When the switch S4 is in the on position, a light emittingdiode 55 illuminates. The power supply 52 is recharged byinterconnection with a 117 volt ac power source. A diode 56 rectifiesthe current to dc through a 4.7K resistor 57.

It will be observed that during operation. on the occurrence of adetecting action as a metallic object passes between the coils. theelectromagnetic field existing therebetween collapses, therebyminimizing the possibility of an electrical force discharging anexplosive device.

We wish it to be understood that we do not consider the inventionlimited to the precise details of structure shown and set forth in thisspecification, for obvious modifications will occur to those skilled inthe art to which the invention pertains.

We claim:

A sealed envelope examining device comprising: a base element forming ahousing, a metal-sensitive oscil lating detector circuit at leastpartially disposed within said housing. said circuit including first andsecond coils developing an electromagnetic field therebetween and analarm device; said base element including a planar upper wall and a pairof side walls on either side thereof, a bridge structure supported byportions of said walls and extending over said upper wall to define aninterstice therebetween for the passage of an envelope therethrough, oneof said coils being supported by said bridge structure, the other ofsaid coils being supported by said base element on opposite sides ofsaid interstice; a slideable drawer element supported by said baseelement and passing beneath said bridge structure, and a pivotallymounted cover element selectively overlying said base element and havingmeans maintaining said drawer element against movement when said coverelement is in overlying position.

2. Structure in accordance with claim 1, including means for mountingsaid upper wall of said base element at an angle relative to horizontal,whereby envelopes placed upon said upper wall may slide under the forceof gravity through said interstice.

1. A sealed envelope examining device comprising: a base element forminga housing, a metal-sensitive oscillating detector circuit at leastpartially disposed within said housing, said circuit including first andsecond coils developing an electromagnetic field therebetween and analarm device; said base element including a planar upper wall and a pairof side walls on either side thereof, a bridge structure supported byportions of said walls and extending over said upper wall to define aninterstice therebetween for the passage of an envelope therethrough, oneof said coils being supported by said bridge structure, the other ofsaid coils being supported by said base element on opposite sides ofsaid interstice; a slideable drawer element supported by said baseelement and passing beneath said bridge structure, and a pivotallymounted cover element selectively overlying said base element and havingmeans maintaining said drawer element against movement when said coverelement is in overlying position.
 2. Structure in accordance with claim1, including means for mounting said upper wall of said base element atan angle relative to horizontal, whereby envelopes placed upon saidupper wall may slide under the force of gravity through said interstice.